Inspection apparatus and inspection method

Abstract

An image acquisition circuit is configured to acquire inspection images based on secondary electrons generated by electron beams emitted to a first area of a sample on a stage. The first area includes sub areas. An estimation circuit is configured to estimate an amount of rotation of an array of the electron beams emitted to the first area based on an amount of misalignment between reference images respectively indicative of patterns to be respectively formed in the sub areas and the inspection images. The stage control circuit is configured to control, based on the amount of rotation, a focus position of the electron beams to be emitted to a second area of the sample. The comparison circuit is configured to compare the reference images with the inspection images.

What is claimed is: 
     
         1 . An inspection apparatus comprising:
 a stage for a sample to be placed;   an image acquisition circuit configured to acquire a plurality of inspection images based on secondary electrons generated by a plurality of electron beams emitted to a first area of the sample, the first area including a plurality of sub areas;   an estimation circuit configured to estimate an amount of rotation of an array of the plurality of electron beams emitted to the first area based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas and the plurality of inspection images;   a stage control circuit configured to control, based on the amount of rotation, a focus position of the plurality of electron beams to be emitted to a second area of the sample; and   a comparison circuit configured to compare the plurality of reference images with the plurality of inspection images.   
     
     
         2 . The inspection apparatus according to  claim 1 , wherein:
 the image acquisition circuit is configured to sequentially acquire a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by a plurality of electron beams emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample and each including a plurality of sub areas, and the estimation circuit is configured to estimate, for each one of the plurality of areas, the amount of rotation of the array of the plurality of electron beams emitted to the one of the plurality of areas, based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas of the one of the plurality of areas and the plurality of inspection images.   
     
     
         3 . The inspection apparatus according to  claim 1 , wherein:
 the plurality of inspection images are based on secondary electrons generated by the plurality of electron beams respectively emitted to the plurality of sub areas on a one-to-one basis.   
     
     
         4 . The inspection apparatus according to  claim 3 , wherein:
 the image acquisition circuit is configured to sequentially acquire a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by a plurality of electron beams emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample and each including a plurality of sub areas, and the estimation circuit is configured to estimate, for each one of the plurality of areas, the amount of rotation of the array of the plurality of electron beams emitted to the one of the plurality of areas, based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas of the one of the plurality of areas and the plurality of inspection images.   
     
     
         5 . The inspection apparatus according to  claim 3 , wherein:
 the estimation circuit is configured to:
 estimate a plurality of first positions in the first area to which the plurality of electron beams respectively have reached, based on an amount of misalignment between each one of the plurality of inspection images and one of the plurality of reference images, and 
 estimate the amount of rotation based on the amount of misalignment between a plurality of initial positions of the plurality of electron beams and the plurality of first positions. 
   
     
     
         6 . The inspection apparatus according to  claim 5 , wherein:
 the image acquisition circuit is configured to sequentially acquire a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by a plurality of electron beams emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample and each including a plurality of sub areas, and   the estimation circuit is configured to estimate, for each one of the plurality of areas, the amount of rotation of the array of the plurality of electron beams emitted to the one of the plurality of areas, based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas of the one of the plurality of areas and the plurality of inspection images.   
     
     
         7 . The inspection apparatus according to  claim 5 , wherein:
 the image acquisition circuit is configured to acquire a plurality of second inspection images based on secondary electrons generated by the plurality of electron beams emitted to a third area of the sample, the third area including a plurality of second sub areas, and   the inspection apparatus further comprises an inspection control circuit configured to estimate the plurality of initial positions of the plurality of electron beams based on an amount of misalignment between a plurality of second reference images respectively indicative of patterns to be respectively formed in the plurality of second sub areas and the plurality of second inspection images.   
     
     
         8 . The inspection apparatus according to  claim 7 , wherein:
 the image acquisition circuit is configured to sequentially acquire a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by a plurality of electron beams emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample and each including a plurality of sub areas, and   the estimation circuit is configured to estimate, for each one of the plurality of areas, the amount of rotation of the array of the plurality of electron beams emitted to the one of the plurality of areas, based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas of the one of the plurality of areas and the plurality of inspection images.   
     
     
         9 . The inspection apparatus according to  claim 7 , wherein:
 the image acquisition circuit is configured to acquire the plurality of inspection images based on secondary electrons generated by emitting the plurality of electron beams in such a manner as to scan each of a plurality of third areas of the sample, and   the inspection control circuit is configured to:
 acquire a plurality of first rotation amounts of the plurality of inspection images, respectively, from a second center point of a set of a plurality of first center points of the plurality of third areas, a vector from the second center point to each one of the first center points, and the amount of the misalignment; and 
 estimate the amount of rotation based on an average of the plurality of first rotation amounts. 
   
     
     
         10 . The inspection apparatus according to  claim 9 , wherein:
 the inspection control circuit is configured to:
 estimate an amount of defocusing of the first area based on the amount of rotation; and 
 control the focus position of the plurality of electron beams by changing a position of the stage to such an extent that the amount of defocusing is canceled. 
   
     
     
         11 . An inspection apparatus comprising:
 a stage for a sample to be placed;   an image acquisition circuit configured to acquire an inspection image based on secondary electrons generated by an electron beam emitted to a first area of the sample;   an estimation circuit configured to estimate an amount of rotation of the electron beam emitted to the first area based on an amount of misalignment between a reference image indicative of a pattern to be formed in the first area and the inspection image;   a stage control circuit configured to control, based on the amount of rotation, a focus position of the electron beam to be emitted to a second area of the sample; and   a comparison circuit configured to compare the reference image with the inspection image.   
     
     
         12 . The inspection apparatus according to  claim 11 , wherein:
 the image acquisition circuit is configured to sequentially acquire a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by an electron beam emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample, and   the estimation circuit is configured to estimate, for each one of the plurality of areas, the amount of rotation of the electron beam emitted to the one of the plurality of areas, based on an amount of misalignment between a reference image indicative of a pattern to be formed in the one of the plurality of areas and the inspection image.   
     
     
         13 . An inspection method comprising:
 acquiring a plurality of inspection images based on secondary electrons generated by a plurality of electron beams emitted to a first area of a sample, the first area including a plurality of sub areas;   estimating an amount of rotation of an array of the plurality of electron beams emitted to the first area based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas and the plurality of inspection images;   controlling a focus position of the plurality of electron beams to be emitted to a second area of the sample based on the amount of rotation; and   comparing the plurality of reference images with the plurality of inspection images.   
     
     
         14 . The inspection method according to  claim 13 , wherein:
 the acquiring includes sequentially acquiring a plurality of inspection images for each one of a plurality of areas based on secondary electrons generated by a plurality of electron beams emitted to the one of the plurality of areas, the plurality of areas being arranged along a first axis of the sample and each including a plurality of sub areas, and   the estimating includes, for each one of the plurality of areas, the amount of rotation of the array of the plurality of electron beams emitted to the one of the plurality of areas, based on an amount of misalignment between a plurality of reference images respectively indicative of patterns to be respectively formed in the plurality of sub areas of the one of the plurality of areas and the plurality of inspection images.   
     
     
         15 . The inspection method according to  claim 13 , wherein:
 the acquiring includes acquiring the plurality of inspection images based on secondary electrons generated by the plurality of electron beams respectively emitted to the plurality of sub areas on a one-to-one basis.   
     
     
         16 . The inspection method according to  claim 15 , wherein:
 the estimating includes:
 estimating a plurality of first positions in the first area to which the plurality of electron beams respectively have reached, based on an amount of misalignment between each one of the plurality of inspection images and one of the plurality of reference images; and 
 estimating the amount of rotation based on the amount of misalignment between a plurality of initial positions of the plurality of electron beams and the plurality of first positions. 
   
     
     
         17 . The inspection method according to  claim 15 , further comprising:
 acquiring a plurality of second inspection images based on secondary electrons generated by the plurality of electron beams emitted to a third area of the sample, the third area including a plurality of second sub areas; and   estimating the plurality of initial positions of the plurality of electron beams based on an amount of misalignment between a plurality of second reference images respectively indicative of patterns to be respectively formed in the plurality of second sub areas and the plurality of second inspection images.   
     
     
         18 . The inspection method according to  claim 17 , further comprising:
 acquiring the plurality of inspection images based on secondary electrons generated by emitting the plurality of electron beams in such a manner as to scan each of a plurality of third areas of the sample; and   acquiring a plurality of first rotation amounts of the plurality of inspection images, respectively, from a second center point of a set of a plurality of first center points of the plurality of third areas, a vector from the second center point to each one of the first center points, and the amount of the misalignment, wherein   the estimating includes estimating the amount of rotation based on an average of the plurality of first rotation amounts.   
     
     
         19 . The inspection method according to  claim 18 , further comprising:
 estimating an amount of defocusing of the first area based on the amount of rotation, wherein   the controlling includes changing a position of a stage to such an extent that the amount of defocusing is canceled.